In recent years, apparatuses using a Doppler radar have been used to measure the trajectory and launching conditions of balls for ball games, and particularly for golf balls (initial velocity, launch angle, and amount of spin of golf balls).
With such apparatuses, a transmission wave comprising microwaves is emitted from an antenna toward a golf ball and a reflection wave that is reflected from the golf ball is measured. Then, based on a Doppler signal obtained from the transmission wave and the reflection wave, the speed of travel and the amount of spin are calculated.
In these cases, the reflection wave must be obtained efficiently in order for the speed of travel and the amount of spin to be measured stably and reliably. In other words, efficiently obtaining the reflection wave is beneficial in the securing of measuring distance.
On the other hand, technology has been suggested for providing a layer or film including a metallic material throughout an entirety of a surface of a ball in order to enhance visual appearance and/or design (see Japanese Unexamined Patent Application Publication Nos. 2007-021204A, 2004-166719A and 2007-175492A).
Additionally, technology has been suggested for providing a metallic layer having a spherical surface shape between a core layer and a cover of a ball in order to ensure energy transfer (see Japanese Unexamined Patent Application Publication No. H11-076458A).
According to the test examples conducted by the present inventors, while beneficial from the perspective of ensuring radio wave reflectivity, when a layer or film including a metallic material is formed in a spherical surface shape throughout an entirety of a surface of a ball, an amount of spin of the ball is insufficient for ensuring measuring distance.